OPERATION METHOD OF EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

PROBLEM TO BE SOLVED: To achieve the operation method of the exhaust emission control device for the internal combustion engine which is operated at lean air/fuel ratio for the main course of its operation. SOLUTION: An exhaust emission control device incorporating a nitrogen oxides storage catalytic converter and a sulfur trap, wherein: a) at the excess air factor higher than 1 and an exhaust gas temperature TK within an activity window ΔTNOX, the nitrogen oxides and the sulfur oxides contained in the exhaust gas are respectively stored on the nitrogen oxides storage catalyst and the sulfur oxides storage catalyst while simultaneously maintaining the exhaust gas temperature TS lower than the desulfurization temperature TS. De SOx and periodically reducing the excess air factor of the exhaust gas below 1 to discharge the stored nitrogen oxides (completion of 1 adsorption cycle); b) after each completion of a predetermined number N1 of cycles of nitrogen oxides adsorption cycle, the exhaust gas temperature TS is raised to a level at or higher than the desulfurization temperature TS. De SOx of the sulfur trap to desulfurize the sulfur trap and to reduce the excess air factor of the exhaust gas to below 1. The process a) and the process b) are periodically repeated.